Frequency modulation of electron discharge devices



L. P. SMITH FREQUENCY MODULATION OF ELECTRON DISCHARGE DEVICES FiledFeb. 14, 1948 INVENTOR LLOYD P. SMITH Java/M a. W

TTORNEY Patented Oct. 21, 1952 FREQUENCY MODULATION ELECTRON DISCHARGEDEVICES Lloyd P. Smith, Ithaca, N. Y., assignor to Radio Corporation ofAmerica, a corporation of Delaware Application February 14, 1948, SerialNo. 8,332

8 Claims. 1

My invention relates particularly to frequency modulation of magnetronsand similar electron discharge devices. However, the principle involvedmay be applied to frequency variation of cavity resonators in general orto varying the capacity between any spaced conductive elements.

The principal object of my invention is to provide a novel method andapparatus for modulating the generated frequency of a magnetron inaccordance with a given signal.

Another object of my invention is to provide novel method and apparatusfor varying the capacitance between two or more spaced conductiveelements. v

Another object of my invention is to provide an improved method andapparatus for varying the resonant frequency of a cavity resonator.

These and other objects will appear hereinafter.

The novel features of my invention are set forth with particularity inthe appended claims, but the invention itself will be best understood byreference to the following description taken in connection with theaccompanying drawing,

in which:

Figure 1 is a perspective view partly cut away of a vane typemulti-cavity magnetron illustrating one embodiment of my invention;

Figure 2 is a top plan view partly in section of themagnetron shown inFigure 1;

Figure 3 is a perspective view similar to Figure 1 of a pole typemagnetron illustrating another embodiment;

Figure 4 is a top plan view in section on the line IVIV of Figure 5 of acavity type magnetron illustrating the application of my invention totwo cavities; and

Figure 5 is a section View taken on the line VV of Figure 4.

The capacitance between certain spaced elements can be varied byproperly moving a conductor relative to said elements. This isconveniently done, in accordance with my invention. by movably mountingthe conductor adjacent said elements, providing a constant magneticfield at right angles to the conductor and passing a current thru theconductor, which results in a force on the conductor at right angles toboth current and field, thereby causing motion of the conductor in thedirection of the force and a consequent change in capacitance betweensaid. elements.

In frequency modulation it is the object to effect a change in thegenerated frequency according to some desired function of the time. Bypassing an alternating current corresponding to a given signal or otherintelligence thru said conductor the resonant frequency of the devicewith which said elements are associated is modulated according to saidintelligence.

Referring to Figures 1 and 2 of the drawing, the vane type cavitymagnetron disclosed therein comprises a cylindrical envelope wall Ihaving integral vanes 2 constituting anode segments and forming a cavityresonator therebetween. Although only two vanes forming a single cavityresonator are illustrated, it will be understood that the completemagnetron will have an even number of vanes 2 equally distributed aroundthe envelope wall I, and that a change in the frequency of one resonatorwill change all the resonators. The inner edges of the vanes 2 arespaced from the center of the structure to define a cylindrical cathodespace, and a cathode C is supported by any suitable means in said space.The usual magnetic field parallel to the cathode and normal to the pathof electrons between the cathode and anode is produced by a permanentmagnet M, Figure 5, or other suitable means. A pair of end plates 3complete the vacuum envelope. It will be understood that the anodestructure I, 2 and cathode C will be maintained at such potentialdifference relative to the magnetic field strength as to produce theusual spoke-like rotating space charge in the cathode space and theoscillating electric fields in the cavity resonators.

The conventional magnetron as described in the preceding paragraph canoscillate in one or more of several different modes, but is, bystrapping alternate vanes together or by other means made to oscillatein the so-called qr-mode Wherein adjacent cavity resonators oscillate130 out of phase at a definite frequency which is determined largely bythe form and dimensions of each cavity resonator. This frequency can bevaried, within certain limits, by increasing or decreasing thecapacitance between the adjacent inner portions of the vanes forming theside walls of the cavity resonators.

In accordance with my invention, each of the vanes 2 is provided at itsinner end with a post 4 extending outwardly therefrom in a directionparallel with the cathode C and the magnetic field. A conductive membersuch as metal bar 5 is movably mounted relative to two adjacent posts 4,in the space between the cover plate :5 and the ends of the vanes 2, bymeans of a flexible metallic strip of which one end is attached a at 1to the envelope wall I and the other end is passed through an insulatingseal 8 in an aperture 9 of the wall I. The distance between the bar andthe ends of the vanes 2 is large compared to the normal spacing betweenthe bar 5 and the posts 4, to minimize the capacitance between theformer. The ends of the bar 5 are electrically connected through thestrip 6, wall I, conductors II and control resistor l2 to a source ofalternating current [0 in accordance with which it is desired tomodulate the magnetron oscillations.

In operation, the current from source Ill passing through the bar 1 atright angles to the magnetic field produces a force on the bar at rightangles to the current and field, that is, toward or away from the posts4, depending on the instantaneous direction of the current in the strip,and the resulting motion of the bar 1 changes the capacitance betweenthe posts 4 and consequently the resonant frequency of the cavityresonator.

Figure 3 illustrates the application of my invention to a pole typemagnetron having asingle cavity resonator formed by a cylindrical wall2i and end plates 22. The anode vanes of Figures 1 and 2 are replaced inthis form of magnetron by an annular series of parallel anode rods orpoles 23 defining a central cathode space. For convenience, only twopoles have been shown. The structure for varying the capacitance betweenthe poles 23 comprises a bar 25 movably mounted relative to the twoadjacent poles shown by means of a flexible metallic strip 25 attachedto the wall 2| at 21 and sealed through an insulator 28 in aperture 29,as shown, and connected by conductors 3| and control resistor 32 withthe modulating source 30. The operation of this embodiment of theinvention is similar to that described above. for Figures 1 and 2, thevariation in capacitance between adjacent poles 23 result ing in acorresponding modulation of the generated frequency of the magnetron.

In Figures 1 to 3, the invention has been applied to changing thecapacitance between two magnetron elements only. However, it can beapplied tov as many elements as desired. In Figures 4 and 5, I haveshown the manner in which two adjacent cavity resonators may beeffectively tuned simultaneously. The envelope 4], vanes 42, cathode C,end plates 43, posts 44, bar 45, strip 46, and insulator 48 are similarto the corresponding elements in Figures 1 and 2. In this form, however,the upstanding posts 44 are circular in cross section and thecapacitance bar 45 is provided with an arcuate recess facing each post,in order that the rectilinear motion of the bar 45 will produce equalchanges in the capacitances between adjacent posts. Obviously, the bar45 may be extended to cooperate with all of the vane posts on one sideof a diametral plane, and another bar may be similarly arranged on theopposite half of the vane structure and connected in series with thefirst bar and the alternating current source, in order to vary directlythe resonant frequency of all of the cavity resonators.

The invention has been illustrated specifically as applied to amagnetron type of electron discharge device, being particularly usefultherein because the existing magnetic .field of the magnetron alsocooperates with the modulating current to produce the desired vibratorymovement of the capacitance bar. However, the invention can be appliedequally well to any cavity resonator or other device with which one isprepared to means for establishing a constant magnetic fieldsubstantially normal to said conductive member and means connecting saidconductive member in series with a source of modulating current.

2. An electron discharge device including a plurality of spacedconductive elements, and means for varying the frequency of said device,by varying the capacitance between said elements, comprising anelongated conductive member movably mounted adjacent said elements andmeans for vibrating said membertoward and away from said elements, saidvibratin means including means for establishing a constant magneticfield substantially normal to said conductive member and meansconnecting said conductive member in series with a source of modulatingcurrent.

3. A magnetron including an annular series of parallel anode elements,an elongated cathode positioned axially of said anode elements, meansfor establishing a constant magnetic field substantially parallel tosaid anode elements and said cathode, and means for modulating thegenerated frequency of said magnetron, by varying the capacitancebetween said anode elements, comprising an elongated conductive membermovably mounted near two adjacent anode elements and lying in a planesubstantially normal to said anode elements, and means extending fromthe ends of said conductive member connecting the latter in series witha source of modulating current, whereby said member is vibrated towardand away from said two anode elements when said magnetic field isestablished and a modulating current is passed through said memberduring operation of said magnetron.

4. A vane type magnetron including a cavity resonator partially boundedby two spaced anode vanes, and means for varying the resonant frequencyof said resonator comprising an elongated conductive member movablymounted adjacent said vanes and means for vibrating said member towardand away from said vanes, said vibrating means including means forestablishing a constant magnetic field substantially normal to saidmember and means connecting said member in series with a source ofmodulating current.

5. A magnetron in accordance with claim 4, wherein each of said vanes isprovided with a projecting pin, and said elongated conductive membercomprises .a block extending across said pins and supported by aflexible strip.

6. A pole-type. single-cavity magnetron comprising a cavity resonatorcontaining a plurality of spaced parallel elongated anode poles extendmgacross said resonator, and means for modulatingthe resonant frequency ofsaid resonator, by varying the capacitance between said poles,comprising an elongated conductive member movably mounted in saidresonator adjacent at least two of said poles intermediate the endsthereof and means for vibrating said member toward and away from saidpoles.

7. A pole-type magnetron including a single cavity resonator containingat least two parallel elongated anode poles, and means for modulatingthe generated frequency of said cavity resonator, by varying thecapacitance between said poles, comprising an elongated conductivemember movably mounted adjacent and across said poles and means forvibrating said member toward and away from said poles, said vibratingmeans including means for establishing a constant magnetic fieldsubstantially normal to said member and means connecting said member inseries with a source of modulating current.

8. A magnetron including an elongated cathode, a plurality of anodeelements adjacent and parallel to said cathode, means for establishing aconstant magnetic field substantially parallel to said cathode and saidanode elements, and means for varying the operating frequency of saidmagnetron, by varying the capacitance between said anode elements,comprising an elongated conductive member movably mounted near two ad 6jacent anode elements and lying in a plane extending transversely ofsaid anode elements, and means connecting said conductive member inseries with a source of modulating current, whereby said member isvibrated toward and away from said two anode elements when said magneticfield is established and a modulating current is passed through saidconductive member during operation of said magnetron.

LLOYD P. SMITH.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,108,640 Bieling Feb. 15, 19382,422,465 Bondley June 17, 1947 2,444,435 Fisk July 6, 1948 2,447,816Rieber Aug. 24, 1948 2,523,286 Fiske et al Sept. 26, 1950

